84 Crossfire - Rough Idle

[joey9011]

Hi All,
I am a newbie Vette owner and first time on this forum… I Just purchased an 84 crossfire Vette with 151k Kilometers. Good shape. Even though there’s a few gremlins I’m still very happy with the purchase.
Picked it up with a ‘rough idle and a miss’, therefore scheduled the usual tune up as the car was stored for the winter… Replaced
- Cap, rotor, ignition module (accel) and coil (accel)
- Replaced plugs (ac delco) and wires (accel)
- Changed oil and oil filter (K & N)
- Changed Air Filter (ac delco)
- Changed Fuel filter
- Changed Pcv

I thought that this major tune up would’ve cleared up the rough idle and miss but the car still idles rough… started the troubleshooting process and noticed that the EGR valve was no longer there and it was replaced with a block off plate.
I therefore went ahead and reinstalled a new EGR valve and installed the proper vacuum tubing to the EGR Solenoid and the TBI. That didn’t resolve the issue.

Since the car is over 26 years old I went hunting for vacuum leaks and didn’t find any (doesn’t mean there aren’t any) and started replacing the tubing that looked frail and damaged. That didn’t help.

Replaced the MAP sensor, no change.

Replaced an IAC with a new one as it broke when I was re-installing it on the TB following a thorough cleaning. No change. (when I set the ECM in diagnostic mode they both keep cycling open\close and won’t stop until I unplug the IAC --- Is this normal??)

Engine idled at 900 rpm in drive therefore, blocked off the idle air passages and Set the min air idle to 500rpm in drive. Readjusted timing from 10 to 6* with EST disconnected and set the TPS at .54. Reconnected everything back up and disconnected the battery to clear error code and started the engine …still a very rough idle at 800 rpm. Took it out for a drive to reset the IAC’s but it didn’t really improve anything. Monitored the Vacuum and the gauge indicated a rock solid 21hg.

The only thing remaining is to replace the Fuel pump and balance the TB’s (and now the heater core as it started leaking coolant in the passenger compartment yesterday)… which should be done over the next few days.

With ALDL cable and Winaldl ran a diagnostics and got the following Sensor data :
RPM 1000 - IAC 80, CT 49, MAP 241 (4.7V, 99.3 KPA), TPS .55v, Int 128, O2 136 (.601 v), Batt 24.9v, Knock Counter 12, BLM 128, Rich/Lean 162

Am I missing something ??
What else can I do to get this great car running fine again ??
Your opinions are very appreciated, thanks.

[c4c5specialist]

HI there,

Check your fuel pressure, you want between 11-13 psi.

Your injectors cannot atomize correctly if its less

Allthebest, c4c5

[joey9011]

Hi c4c5specialist,

Since the car is 26 years old, I picked up a new replacement fuel pump this morning and will do the swap later today... I also replaced the fuel pump relay (yesterday), good thing, as I disconnected the connector at the FPR most of the wires had approximately half inch of conductor exposed and each of the wires were touching one another.

Will chime in to give you an update once this is completed.

Do you see anything else that I should take a look at ??

[ChuckG]

Your battery reading was 24.9v??? Maybe 12.9v, but 24.9v is higher than I've ever heard.

While you're at it, maybe a bottle of Techtron in the next few tanks or have the injectors professionally cleaned.

Who knows what quality gas the car has been fed all these years?

[joey9011]

Hi ChuckG,

When running Winaldl the reported battery reading was actually 24.9V... I took the measurements with a good old Voltmeter and the reading was at 14.3 as reported on the instrument panel...
Another weird one is the MAP reporting at 241 and CT at 49.

Would you think that I probably have an ECM issue ???

As for the gas additive.... I've already poured in a good amount of Seafoam and plan to do this over the next few gas fillups.

Thanks

[ChuckG]

Seafoam is a no-no. It softens plastics and I don't think is sensor-safe. Techtron is the way to go.

If you're worried about carbon build up, BG44K.

14.3V is enough to make me shut it down and throw on a battery charger. Anything over 13.5v and then only briefly, makes me nervous. I've toasted alternators letting them charge a battery that's too discharged before I knew better.

Far as the ECM. I dunno. That's a tough one. Not that familiar with the 1984 boxes. My '85 is known to have a weak one so in my yearly "laundry list" of things to address just as routine maintenance I replaced mine a few years ago. Far as I can tell, $90 spent now is better than being stranded later.

But rest assured, you have come to the right place. Give good accurate data to C4C5 Specialist and he'll be able to set you on a strong course of action.

[joey9011]

Hi ChuckG,
OK, I'll stop using seafoam and I'm not really worried about carbon build up.

Same thought as yours, I did put a battery charger on and it tells me that it's fully charged... what do you recommend ??

As far as ECM. I agree with you, that's why I'm picking one up tommorrow afternoon.

Thanks

[ChuckG]

Personally? I'd get the battery to a reputable shop and have it evaluated. Do you know how old it is and how it's been maintained? Batteries don't thrive when just left alone with no maintenance. I use a trickle charger and it's been a great investment for Winter storage.

Next, I'd consider a full charging system test, but that's me. I've lost alternators over the years because their failures can be less than total, but still harmful.

[ChuckG]

If it comes to pass, this place comes highly recommended by folks on the Corvette Action Forum. I;m buying my injectors from them today.

Fuel Injector Restoration Service - Throttle Body Injector Service - Fuel Injector Connection

[joey9011]

Originally Posted by c4c5specialist

HI there,

Check your fuel pressure, you want between 11-13 psi.

Your injectors cannot atomize correctly if its less

Allthebest, c4c5

Hi c4c5specialist,

I still have a rough Idle....

I replaced the fuel pump, measured the fuel pressure and it's steady at 13psi...

I verified the grounds and the charging system which is fine according to the FSM... at 13.1 - 13.4V.

When running winaldl I still have the same type of numbers as above with respect to IAC, MAP and Voltage. This is starting to look like a marginal ECM...

The last thing I have left to do is balance the TB's ... could this be my problem or am I going in the wrong direction ??

Thanks and appreciate your comments.